Nonaqueous lithium secondary batteries including a positive electrode and a negative electrode that were capable of occluding and releasing lithium ions and a nonaqueous electrolytic solution in which a lithium salt, e.g., LiPF6 or LiBF4, had been dissolved were developed, and are in practical use. Although various negative-electrode materials for use in these batteries have been proposed, use is being made of graphitic carbon materials such as natural graphites, artificial graphites obtained by graphitizing, for example, cokes, graphitized mesophase pitch, graphitized carbon fibers, etc., because of advantages thereof, such as a high capacity and excellent flatness of discharge potential.
Also used is amorphous carbon materials, for example, for the reason that the carbon materials are relatively stable to some electrolytic solutions. Furthermore, a carbon material which was obtained by causing amorphous carbon to cover or adhere to the surface of graphitic carbon particles and which has been thereby made to combine the properties of graphite and the properties of amorphous carbon is in use.
In patent document 1 is used a rounded graphitic carbon material which was obtained by subjecting graphitic carbon particles, which in themselves are flaky, scalelike, or platy, to a mechanical energy treatment to damage the surface of the graphitic particles and simultaneously make the particle shape spherical and which has been thereby made to attain improved high-rate charge/discharge characteristics. Furthermore, proposed therein is to use a multilayered rounded carbon material which was obtained by causing amorphous carbon to cover or adhere to the surface of the rounded graphitic carbon particles and which has been thereby made to combine the properties of both graphite and amorphous carbon and high-rate charge/discharge characteristics.
Patent document 2 discloses that a battery having excellent high-rate charge/discharge characteristics is obtained by using, as an electrode, a multilayered carbon material which was obtained by causing amorphous carbon to cover or adhere to the surface of graphitic carbon particles and in which the amount of CO eliminated therefrom during heating to 800° C., as determined with a temperature programmed decomposition mass spectrometer (TPD-MS), is 0.8×10−6 mol/g to 30×10−6 mol/g.
However, as a result of the recent development of applications of nonaqueous lithium secondary batteries, there is a desire for a nonaqueous-electrolyte secondary battery that combines high-rate charge/discharge characteristics and high cycle characteristics and that is for use in notebook type personal computers, mobile communication appliances, portable cameras, portable game machines, and the like, which are expected to have higher performances than before, and for use in power tools, electric vehicles, etc.
Meanwhile, although battery production includes the step of infiltrating an electrolytic solution into the electrodes disposed in a battery can, the prolonged time period required for the electrodes to absorb the electrolytic solution is a cause of an increase in production cost.